1. Field of the Invention
The present invention generally relates to a mobile communication system including a base station and mobile communication apparatuses such as portable telephones, and a mobile communication apparatus used in such a system. More particularly, the present invention relates to a mobile communication system and a mobile communication apparatus in which a wait time is extended.
A mobile communication apparatus such as a portable telephone has a built-in battery or is detachably coupled to a battery. Call origination, call proceeding and call incoming are controlled using the operating power supplied by the battery. The base station calls a mobile communication apparatus at predetermined intervals so that an extended wait time of the mobile communication apparatus is insured by supplying the power from the battery at the same intervals as the intervals at which the base station calls the mobile communication apparatus. Given the same wait time, such an approach is effective in reducing the size and weight of the battery. There is a demand for extending the wait time of the mobile communication apparatus.
2. Description of the Related Art
The format of transmission from a base station is such that 36 subframes constitute 1 superframe, wherein one subframe has a duration of 20 ms so that 1 superframe has a duration of 720 ms. Generally, 1 subframe in 1 superframe is used to call a mobile communication apparatus. The subframe used to call the mobile communication apparatus (hereinafter, referred to as a call subframe) is identified by announcement information from the base station. The mobile communication apparatus in a zone served by the base station performs intermittent reception such that the operating power is supplied for 20 ms immediately preceding the call subframe, from a battery to a radio reception unit. Upon detecting the call, the mobile communication apparatus generates a ringing tone and responds to the incoming call, whereupon speech communication proceeds.
The base station transmits announcement information adapted for the base station. As shown in FIG. 1A, the announcement information contains information items including a message type, a network number, regulation information, control channel construction information, designated transmission power for transmission to a mobile station, a wait enable level, a wait deterioration level, multiplicity of location registration areas, the maximum number of report channels, the number of perch channels for determining zone/sector, a location registration timer, extended information items and the like.
As shown in FIG. 2B, the control channel construction information items include Np, Nc, Ab, Ap, As1, As2, F.sub.1, S.sub.1 -F.sub.NC, S.sub.NC, where Np indicates the number of groups of mobile stations per a channel, Nc indicates the number of control channels in a zone (including the perch channels), Ab indicates the number of BCCH (announcement channel) slots per a control channel, Ap indicates the number of PCH (control channel) slots per a group, As1 indicates the number of SCCH (control channel) slots succeeding BCCH, As2 indicates the number of SCCH slots succeeding PCH, F.sub.1, S.sub.1 -F.sub.NC, S.sub.NC indicates frequency codes of the control channels and slot numbers.
A mobile station enters a wait state in a perch channel, based on the control channel construction information contained in the announcement information. The mobile station may also switch from the perch channel to a designated control channel. Since 1 subframe of the 36 subframes in a 720 ms superframe is used as a call subframe, the maximum intermittent reception ratio in the conventional mobile station is 20/720=1/36. Thus, the wait time is extended as compared to a case where the battery continually supplies an operating power.
In a mobile communication system, the frequency of call incoming to the mobile station (mobile communication apparatus) may vary depending on the behavior of users. Generally, the frequency of call incoming also varies significantly depending on the time zone and the area. It is also to be noted that reduction of the battery size is also requested in addition to the extension of the wait time. However, the conventional mobile station only achieves extension of the wait time by setting the intermittent reception ratio to, for example, 1/36, as described above. Further extension of the wait time has not been available.